1. Field of the Invention
The present invention relates to radio frequency monolithic integrated circuits, and particularly to a radio frequency monolithic integrated circuit for use in radiocommunication terminal transmitters such as cellular phones.
2. Description of the Related Art
There are known conventional semiconductor devices having a structure in which a transistor is formed on a silicon layer (SOI (Silicon On Insulator) layer) having high resistivity which is bonded onto a conductive silicon substrate through an insulation film therebetween, and a specified terminal of the transistor and the conductive silicon substrate are electrically connected by a plug structure penetrating through the SOI layer. Among them, a prior-art example closest to the present invention is disclosed in Japanese Patent Laid-open No. 7-283414.
In the prior-art example, an MOS transistor is formed on the SOI layer on the conductive silicon substrate. The MOS transistor is formed on the SOI layer in order to completely deplete the portion directly beneath a diffusion layer and the portion directly beneath a channel region, thereby reducing the parasitic capacitance. A hole penetrating through the SOI layer to reach the conductive silicon substrate is bored, and a conductive material is buried in the hole to form the plug structure. The source of the MOS transistor is connected to the plug structure, resulting in that the conductive silicon substrate as a ground and the source are electrically connected to each other.